1. Field of the Invention
The present invention relates to an adhesive composition. In particular, the present invention relates to an .alpha.-cyanoacrylate base adhesive composition having good storage stability.
2. Description of the Related Art
Since an .alpha.-cyanoacrylate base adhesive is a reactive adhesive comprising an .alpha.-cyanoacrylate monomer, it tends to be cured in an adhesive container during storage because of radical or anionic polymerization of said monomer. Therefore, a polymerization inhibitor is added to the adhesive as a stabilizer to improve the storage stability of the adhesive.
As the radical polymerization inhibitor for the .alpha.-cyanoacrylate monomer are used hydroquinone, hydroquinone monomethyl ether, catechol, pyrogallol, bisphenol A and the like. The polymerization inhibitor is added to the adhesive in an amount of 1 to 5000 ppm to inhibit the radical polymerization during room temperature storage.
The anionic polymerization is initiated with a small amount of moisture or a base such as an amine and ammonia. To prevent increase of viscosity and gelation due to anionic polymerization of the monomer are used SO.sub.2, SO.sub.3, SOCl.sub.2, SO.sub.2 Cl.sub.2, HF, BF.sub.3, BF.sub.3 -ether complexes, NO.sub.2, paratholuenesulfonic acid, methanesulfonic acid, propanesultone, phosphoric acid, sulfuric acid and the like.
However, the addition of the anionic polymerization inhibitor increases the setting time of the adhesive and deteriorates instantaneous adhesivity. Since such inhibitors are in a gas state at ambient temperature, their handling and adjustment of their concentration in the adhesive are difficult. Some of them such as SO.sub.3 and BF.sub.3 -ether complexes tend to fume and color the adhesive.